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these programs can propagate. In an environment like a university campus, where anyone has access to any computer and programs are routinely carried from machine to machine on diskette, they can breed exponentially. They are, after all, designed to replicate – so one copy quickly becomes two, two become four, four become eight, and so on. Dellinger found that once let loose, the programs’ spread was almost unstoppable.

It was another four years, though, before self-replicating programs became ‘viruses’. The term was first used in a series of short stories written in the 1970s by David Gerrold. In 1972 the author expanded on the virus theme for a sci-fi novel called When HARLIE was One. HARLIE was a Human Analogue Robot Life Input Equivalents computer, a form of artificial intelligence that could duplicate every function of the human brain. This electronic mind could also dial up other computers by telephone and reprogram them or modify data. In so doing, HARLIE was emulating a computer program called simply Virus, which dialled up telephone numbers at random. When it found another computer at the end of the line, it loaded a copy of itself on to the new machine – which started dialling other computers to transfer copies of the program, and so on. Soon hundreds of computers were tied up randomly calling numbers.

The term acquired academic currency in 1985 when a graduate student at the University of Southern California named Fred Cohen completed his dissertation on self-replicating programs. At the suggestion of his adviser, he decided to call them ‘computer viruses’. It seemed a snappier name. A virus, he wrote, is ‘a program that can infect other programs by modifying them to include a slightly altered copy of itself.’ Further, ‘every program that gets infected can also act as a virus and thus the infection grows.’ Cohen also indicated that viruses presented a threat to computer security and could modify or damage data.

The thesis did not break new grounds in terms of computer science: in essence, Cohen took the known characteristics of self-replicating programs and renamed them viruses. The term itself suggest that the programs are created in some uncontrollable electronic biosphere, that they form a sinister plague that is spread unstoppably from computer to computer – a high-tech equivalent of the biological AIDS

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